I tried uploading a 1.4 MB profile image but I got a dialog
Sorry, that file is too big (maximum size is 4 MB). Why not upload your large file to a cloud sharing service, then paste the link?
I set up an avatar on gravatar.com with the same email address as this discourse account and tried using the avatar option and got
Sorry, we can't find any avatar associated with that email address. Can you try uploading it again?
How do you get an image working with the discourse profile?
I took the liberty to retag your question as it seems to be related to this site and not to a specific problem with LO usage.
If I’m wrong, tell me in a comment.
AFAIR (IIRC) avatars are not pulled from gravatar .com but https://www.libravatar.org/ instead. Yes, the description in the “Change your profile picture” dialog would be wrong then (and maybe not configurable). I might be wrong, but I don’t remember having added the email address I use to the pest hole of Attic/Wordpress which Gravatar is.
The simplest may be to upload a small picture from your profile management dialog. Anyway, a 4 MB will be rejected. So, make a reduced version of your picture in an image program like GIMP to scale it to the reduced size and pixel density.